1. Field of the Invention
The present invention relates to a method and an apparatus for inspecting the condition of a splice at the portion of an elongate sheet such as a magnetic tape where two lengths of the sheet or tape are connected together and more particularly to a splice inspection method and apparatus suitable for use in the case of, for example, splicing a magnetic tape and a leader tape by means of a splicing tape, for the purpose of inspecting for transverse displacement between the magnetic and leader tapes, overlapping of the tapes, separation between the ends of the tapes and the like.
2. Description of the Prior Art
In the production of audio and video tape cassettes and the like, a leader tape (or trailer tape) is spliced to a magnetic tape by use of a splicing tape. Up to now, determination of whether any transverse displacement, overlapping or separation existed between the two tapes at the splice was left entirely up to visual inspection by the operator.
When visual inspection is relied on, however, there are likely to arise differences in judgment between operators and a tired operator may overlook a faulty product completely. These and other problems make it difficult to maintain a consistent product quality. Moreover, the need to use an operator increases personnel costs, which are reflected in the cost of the product, while the inclusion in the production process of a step carried out by a human being slows down the overall production speed.
As one way of overcoming these problems it might be considered to irradiate the splice region of the tape as the tape is moved in its lengthwise direction, receive the light reflected from or transmitted by this region, and automatically judge the quality of the splice condition by comparing the light quantity information obtained in this way with a prescribed reference value. With this method, if a planar sensor such as a CCD (charge-coupled device) should be used as the means for detecting the reflected or transmitted light, it would be possible to judge the quality of the splice with high accuracy by comparing the information pattern obtained from the planar sensor with a prescribed pattern.
Since planar sensors are expensive, however, the use of such a device would increase the product cost. Moreover, for judging quality with respect to a wide range of different splice conditions it would be necessary to employ sophisticated pattern recognition techniques, which would require a complex inspection software program and lengthen the inspection time.
Another method that might be considered is that of disposing a one-dimensional light sensor so that its lengthwise direction coincides with the transverse direction of the tape, detecting transmitted or reflected light from the whole width of the tape, and judging the quality of the splice from changes in the magnitude of the total light quantity detected. With this method the cost of the light sensor would be lower than in the case of using a CCD or the like and the software required would also be simpler.
With such a method, it would be easy to judge the splice quality as regards overlapping of the tape ends (since the quantity of light received would vary with difference in transmittance or angle of reflection) and as regards separation between the tape ends. However, a complex inspection method would be necessary for determining the splice quality as regards alignment/misalignment of the two spliced tapes in their transverse direction since changes in this alignment would not produce changes in the total quantity of transmitted or reflected light. It might in fact become necessary to provide one system (combination of apparatus and software) for detecting the splice quality as regards transverse displacement and a separate system for detecting splice quality as regards other factors. This would increase the overall cost of conducting the inspection and also increase the inspection time.